Refactoring and new spec test

[enemarke]

I have moved changes in /lib/* and /manifest/* and their spec from #120 test into this pull req.

[mcgege]

@enemarke I just checked out your PR in my test environment and tried it on three different systems (centos 7, opensuse 42.3, ubuntu 16.04 / puppet version 5.3.3) - on all systems I get an error:

Error: Could not retrieve catalog from remote server: Error 500 on SERVER:
Server Error: Evaluation Error: Error while evaluating a Resource Statement, Evaluation Error:
Unknown function: 'combine_sugid_lists'. at [...]/os_hardening/manifests/suid_sgid.pp:114:22 on node

[enemarke]

Sorry my mistake. In this branch I forgot to move the function to the correct folder. That should now be fixed.

[mcgege]

Looks good now, thank you!